Don't understand how the Speedbooster Works? Here it is in a single diagram.

While the speedboosters have been out for quite a while now, I still regularly see people expressing confusion as to how they work in making the lens wider. Maybe this could be a useful reference point...

Today I was enjoying reading the Google Translate version of an article by Marco Cavina entitled (in English): "A Tribute to the Legendary Immortal Kubrick and the Planar 50mm f/0.7." It's an excellent article, as all of Cavina's are. But this image struck me as particularly useful in helping to convey how the Speedbooster works. The famous Planar 50mm f/.7, also used a "speedbooster" in its design, though the technical term is converging lens group.

So here it is: How a Speedbooster/converging group functions:
It's clear here that the converging group has the opposite function as a teleconverter.

Beyond that, the article itself in its google translate form is still quite engaging, if you have the time.

Just a quick question on boosting lenses for M4/3 sensors. Am I correct that there are yet no booster adapters available for M4/3 sensors, but just adapters with M4/3 mount that focus the full frame image to fit an APS-C size sensor? So a significant part of the image is still wasted if I use any of the current booster adapters on my M4/3 camera?

Just a quick question on boosting lenses for M4/3 sensors. Am I correct that there are yet no booster adapters available for M4/3 sensors, but just adapters with M4/3 mount that focus the full frame image to fit an APS-C size sensor? So a significant part of the image is still wasted if I use any of the current booster adapters on my M4/3 camera?

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Yes and no. On an APS body you can only use Full Frame lenses or you get vignetting. BUT on a m4/3 body you can use both FF and APS lenses. So although you do loose a little with the FF you gain the ability to use APS. Also what you loose with the FF lenses are the distorted and less focused edges.

Yes and no. On an APS body you can only use Full Frame lenses or you get vignetting. BUT on a m4/3 body you can use both FF and APS lenses. So although you do loose a little with the FF you gain the ability to use APS. Also what you loose with the FF lenses are the distorted and less focused edges.

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I think it's a bit more complicated than that. With a SpeedBooster, a FF lens on an APS-C sensor gives a slightly narrower (1.1x) angle of view than that same lens on a full frame camera. With the same lens and SpeedBooster on a mFT sensor, you get a significantly narrower (1.42x) angle of view than with the lens on a FF camera. Lastly, with a SpeedBooster, an APS-C lens gives a slightly wider (0.91x) angle of view than with the lens on an APS-C sensor.

In short, the FF lens will have its corners cropped in both cases, just substantially more so on mFT than APS-C, and the APS-C lens will actually have worse edges on the mFT sensor than natively, since you're using more of the imaging circle than any native APS-C sensor.

Just a quick question on boosting lenses for M4/3 sensors. Am I correct that there are yet no booster adapters available for M4/3 sensors, but just adapters with M4/3 mount that focus the full frame image to fit an APS-C size sensor? So a significant part of the image is still wasted if I use any of the current booster adapters on my M4/3 camera?

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I suppose you could put it that way. But I don't know if its entirely accurate. The issue is one of space. You just can't get a .5x converging group into the space between the sensor and the SLR lens. Nevertheless, the Metabones μ43 Speedbooster may not be .5x, but it is explicitly designed for getting highest resolution it can for a μ43 sensor. Brian Cadwell stated that the μ43 version is actually superior to the APS-C version for NEX and Fuji X.

In short, the FF lens will have its corners cropped in both cases, just substantially more so on mFT than APS-C, and the APS-C lens will actually have worse edges on the mFT sensor than natively, since you're using more of the imaging circle than any native APS-C sensor.

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You'll see the corners getting clipped on my Sigma 18-35 f/1.8A but it isn't that bad: (Defocused, unevenly lit ceiling used but you'll see the corners)